Wall Street’s biggest banks have largely avoided investing directly in cryptocurrencies. But many are quietly working to integrate blockchain, the technology behind crypto, into trading and other businesses.

Goldman Sachs GS -1.74% Group Inc. is already trading some bonds and other debt securities for clients on blockchain-based networks such as Ethereum, and the bank is building its own blockchain-based trading platform. JPMorgan Chase JPM -1.64% & Co. already has a platform in place, called Onyx.

Big Wall Street firms help make the economy run, connecting buyers and sellers of securities and lending money to businesses. But their sophisticated trades are often run on creaky old systems. Goldman and others hope they will be able to run faster, less-costly and ultimately more-profitable systems based on blockchains.

The blockchain, sometimes called distributed ledger technology, is the plumbing that keeps crypto markets running. It is basically a software program that uses an open record-keeping system—a central ledger—to track assets and record transactions and information about ownership of those assets. Every participant operates off the same central ledger.